This invention relates to motors or actuators having variable air gaps and an eccentrically positioned epicyclic transmission.
Prior art motors and actuators have utilized a rotor that is eccentrically positioned relative to the central axis of the actuator and constrained to orbit about a small radius which is typically 3/64 inch (1.2 mm). The orbit radius is determined, inter alia, by the eccentric distance. Typically, these actuators comprise a rotor which operatively drives a floating ring gear, which may, in turn interact with a stationary gear that is mounted to the housing. However, a ring gear that is positioned in a floating relationship between the stationary gear and output gear will show a tendency to jump out of gear mesh and bind. In operation, the reaction forces between the ring gear and the stationary gear causes the ring gear to rotate relative to the stationary gear. The ring gear is drivingly connected to and turns an output gear. In electric actuators, the eccentricity, or the orbit radius, must be small to maintain a small air gap for efficient actuator operation. Typically the ring gear is driven by the rotor consequently the ring gear and the remaining portions of the epicyclic gearing or transmission have the same eccentricity. The prior actuators, were low power transmition devices, consequently, small eccentric gearing did not represent a severe problem. Because of these small eccentricies, the gearing often comprised fine pitch gears which are not satisfactory for transmitting high power. Conversely, high torque devices employ larger air gaps which tend to decrease the efficiency of operation of the motor.
An object of the present invention is to provide a motor or actuator having a rotor that orbits about a small radius for efficient electric operation while simultaneously permitting the ring gear to rotate about a larger eccentric distance thereby permitting the utilization of gears designed to transmit high levels of torque.
A feature of the present invention is a double eccentric which is a mechanism that is free to rotate about a set of support bearings. The double eccentric causes the rotor and the ring gear to move with an eccentric motion of varying degree.
An advantage of the present invention is that the double eccentric, rotor and ring gear may be configured such that the motion of the rotor and ring gear move oppositely, thus dynamic balancing the motor.
According to the embodiments of the invention as described below, the invention comprises an electric motor or actuator having a housing and a stator mounted to the housing about a central axis. The stator includes a plurality of stator poles having at least one coil wound thereabout for developing a magnetic field in response to activation signals input to a particular coil. In one embodiment the actuator includes a rotor that is mounted within the housing in surrounding relationship to the stator for moving in an orbiting manner with respect to the stator poles in response to the magnetic force. The rotor has an axis that is eccentrically positioned from the central axis by a distance e.sub.1 and further includes a double eccentric that is mounted in rotating, surrounding relationship to the rotor and drivingly coupled thereto for transmitting the motion of the rotor to a ring gear. The double eccentric includes a cylindrical first or inner surface surrounding the rotor and has an axis that is coaxial to the axis of the rotor and further includes a cylindrical second or outer surface having another axis that is eccentrically positioned from the central axis by a distance e.sub.2. Drive bearings are concentrically positioned with respect to the inner surface of the double eccentric and interpose the inner surface of the double eccentric and the outer surface of the rotor. The drive bearings transmit the motion of the rotor to the double eccentric. The actuator additionally includes a ring gear that is positioned in surrounding relationship relative to the second surface of the double eccentric and is mounted coaxially with respect to the axis of the outer surface of the double eccentric. The ring further includes a plurality of sets of gear teeth that are disposed about an outer surface and wherein the rotor further includes an inner surface. The second set of drive bearings interposes the inner surface of the ring gear and the outer surface of the double eccentric. This second set of drive bearings transmits the driving force from the double eccentric to the ring gear. A stationary gear is attached to the housing and is mounted in surrounding relationship to the ring gear. The stationary gear includes a set of gear teeth which react with a coacting set of gear teeth on the ring gear, thus causing the ring gear to turn in response thereto. The rotating motion of the ring gear is transmitted to an output gear which is mounted in surrounding relationship to the stator gear and to the ring gear.
An alternate embodiment of the invention is also described which describes an electric actuator which utilizes an output gear which is disposed along the central axis of the actuator.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.